Steam generator

ABSTRACT

A steam generator for receiving heating gas at a temperature exceeding 750*C. The generator comprises an upright housing having a gas inlet in the lower end and a gas outlet at the upper end. An upper tube sheet is spaced below the gas outlet and a lower tube sheet is spaced above the gas inlet. An intermediate tube sheet is spaced below the upper tube sheet to provide a suitable steam space from which steam is discharged from the housing. Heating gas tubes have their ends fixed to the upper and lower tube sheets and pass freely through the intermediate tube sheet. Water is introduced into the housing in the region directly above the lower tubesheet. Surrounding, and spaced from each heating gas tube, is a steam guide tube, the upper end of which is fixed to the intermediate tube sheet. The lower end of each guide tube extends into a protective cup, the lower end of which embraces and is fixed to the respective guide tube, and the upper end of which is open and disposed above the highest liquid level in the housing. Means are provided for militating against vibration of the steam guide tubes.

v United States Patent 91 1111 3,867,907

Marsch Feb. 25, 1975 STEAM GENERATOR [75] Inventor: Hans-Dieter Marsch, ABSTRACT Dortmuhd'oespels Germany A steam generator for receiving heating gas at a tem- [73] Assignee: Friedrick Uhde GmbH, Dortmund, P f exceeding 9 Comprises Germany an upr1ght housmg havmg a gas mlet 1n the lower end and a gas outlet at the upper end. An upper tube sheet [22] Flledi June 1974 is spaced below the gas outlet and a lower tube sheet [21] Appl. No.: 475,624 is spaced above the gas inlet. An intermediate tube sheet is spaced below the upper tube sheet to provide a suitable steam space from which steam is discharged [30] Forelgn Apphcamm Prlomy Data from the housing. Heating gas tubes have their ends June 16,1973 Germany 2330705 fixed to the upper and lower tube sheets and pass freely through the intermediate tube sheet. Water is [52] U.S.Cl 122/34, 122/491 introduced into the housing in the region directly [51] Int. Cl. F22b 1/06 above the lower tubesheet. Surrounding, and spaced [58] Field of Search 122/32, 34, 483, 488, 491 from each heating gas tube, is a steam guide tube, the upper end of which is fixed to the intermediate tube [56] References Cited sheet. The lower end of each guide tube extends into UNITED STATES PATENTS v a protective cup, the lower end of which embraces 3,049,105 8/1962 Waldron 122/483 and is fixed to the respective guifie tube and the 3,097,630 7/1963 Kinyon et al. 122/34 W end 0f which is Open and dlsposed ahve the 3,116,721 1/1964 Huet 122/488 x highest liquid level in the housing- Means are Provided 3,557,756 l/l971 Romanos et a]. l22/483 X for militating against vibration of the steam guide Primary Examiner--Kenneth -W. Sprague Attorney, Agent, or Firm-Malcolm W. Fraser, Esq.

GAS OUT LET tubes.

4 Claims, 2 Drawing Figures STEAM H DISCHARGE 8 7 WATER I, I "'mLeT PAIEMEQFEMSETS 57 997.

GAS OULET WATER GAS iNLET l STEAM GENERATOR BACKGROUND OFTHE INVENTION Process gases, hereinafter referred .to as heating gases, are frequently obtained at elevated pressure and temperature levels in chemical plants. As the high temperature level is often unsatisfactory for subsequent process steps,.the gases must be cooled. The heat to be dissipated is transferred at the maximum possible efficiency to another fluid, for example steam for general purpose service. Considerations referring to plant operation call for safe and intensive cooling. In addition, a fluid of high temperature level is intended to raise the temperature of another fluid to a high level, the heat transfer being dependent on a favorable temperature difference.

The cooling of hot synthesis gases from reactors for partial oxidation may be cited as a typical example. For the manufacture of 1000 tons/day of ammonia, gas is produced at a rate of 100.000 Nm /hr. in a reforming reactor at a temperature of approximately l350 C,'and a pressure of, for example, 50 atm. abs. Cooling is performed in a steam generator of special design with the hot gas passing through the tubes. The heating gas tubes are fully submerged in water which is at a pressure of, for-example, 120 atm. abs. The vaporizing temperature of the water corresponding to this pressure is 323 C. The heating gas tubes within the steam generator are arranged in such a way that they do not penetrate through the surface of the feed water to be vaporized. The saturated steam produced is not suitable for general purpose application because it will be subject to immediate condensation upon the slightest cooling, for example in expansion machines. Problems are even likely to arise in using this saturated steam as a heating agent for another process fluid because the steam is generally required to be transferred to a separate item of equipment. The loss of heat occurring necessarily on the transfer route will cause premature condensation and, consequently, constitutes a substantial loss of thermalenergy. Where superheated steam is intended to be produced with the aid of heating gases, it has so far been common practice to send the saturated steam into a separate item of equipment where the heating gases are utilized for superheating the steam. The problem, therefore, consists in providing for simultaneously superheating the saturated steam in the same item of equipment in which the heating gas tubes penetrate through the fluctuating water surface for the subsequent superheating of the saturated steam.

It is known that the heating gas tubes are subject to rapid deterioration in the transition area between water space and steam space. This deterioration is mainly due to the thermal shock, which is attributable to the fluctuating water level and the impact of splashes of boiling liquid upon the tubes. Although the temperature of the heating gas in the tube is far beyond 750 C, the wall temperature of the heating gas tubes is only about 400 C. The boundary layer of the hot gas stream is subject to a strong temperature drop towards the tube wall, this temperature drop being caused through the intensive cooling by the water surrounding the tubes in the water space. Above the liquid level, the tubes are contacted by substantially stagnant saturated steam. Due to the poor heat transfer between tube and saturated steam, the tube wall temperature is not sufficiently lowered in LII the steam space. Consequently, the tubes are exposed to a particularly high temperature in the transistion area between liquid level and steam space. Because of the fluctuating liquid level, the tubes are also subject to high alternating thermal stresses. A protective oxide layer cannot build up on the outsidesurface of the gascarrying tubes because it will peel off steadily. The deterioration then appears as corrosive attack. The service life of such steam generators is markedly limited.

SUMMARY OF THE INVENTION The present invention relates to a steam generator with heating gas tubes and with liquid and steam spaces to receiving heating gas at'a temperature exceeding 750 C. Steam generators of this type are preferably used for producing steam at elevated pressures and temperatures.

The object of the present invention is to providea steam generator with heating gas tubes receiving heating gas at a temperature exceeding 750 C for simultaneously producing superheated steam while avoiding the disadvantages of known designs as outlined above.

According to this invention, the problem is solved in that the steam space is provided with an intermediate tubesheet, the steam outlet nozzle being arranged above said intermediate tubesheet, the heating gas tubes being arranged with part of their length surrounded by the liquid while the upper part extends through the liquid surface and the tubes penetrating through the intermediate tubesheet, the heating gas tubes being surrounded by steam guide tubes in the lower part of the steam space, the upper end of said steam guide tubes terminating in the intermediate tubesheet while the lower ends are surrounded by protective cups fitting closely to the heating gas tubes below the lowest liquid level and being open above the highest liquid level so that an annular space remains between heating gas tubes and steam guide tubes and between steam guide tubes and protective cups. In order to prevent the lower ends of the steam guide tubes from being subject to vibration, they are fixed in the protective cups by common means.

The invention incorporates the particular advantage that superheated steam of any desired temperature level can be produced in a steam generator without any need of routing the heating gas tubes to a superheater outside the steam generator. In addition, the heating gas may be at a very high temperature level without any risk of thermal shock with consequent corrosive attack on the heating gas tubes.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings illustrate an example of application that may be described in more detail as follows:

FIG. 1 is a schematic representation of a steam generator with superheating section; and

FIG. 2 is an enlarged sectional view of a single tube assembly in the area of the fluctuating liquid level and showing retaining pins for the steam guide tube.

DESCRIPTION OF THE PREFERRED EMBODIMENT Steam generator 1 of FIG. 1 comprises a heating gas tube system having an upright housing containing spaced heating gas tubes 2, which communicate through vertically spaced tube sheets 3 and 3a to a heating gas inlet nozzle 4 and a heating gas outlet nozzle 5. The several tubesheets are connected in fluid tight manner to the sides of the housing. Feed water is admitted through nozzle 6 into the liquid space while steam is discharged through nozzle 7. The steam space is partitioned through intermediate tubesheet 8 into a lower steam space 9 which is in direct contact with the liquid, and an upper steam space 10. The lower part of the heating gas tubes 2 that is cooled by the surrounding feed water operates as the vaporizer section. These tubes may also be of coiled or helical shape.

In the area of the fluctuating liquid level 11, the heating gas tubes 2 are surrounded by protective cups 12 so that the liquid level does not reach the heating gas tubes. The protective cups 12 fit closely to the heating gas tubes 2 in liquid tight relation below the lowest liquid level. The upper part of the heating gas tubes 2 is surrounded by steam guide tubes 13 whose upper end is fixed to the intermediate tubesheet 8 while the open lower end terminates in the protective cups 12.

This design imposes a defined route upon the steam accumulating in the steam space 9, in that the steam first passes downwards into protective cups 12 for subsequently arriving, after reversal of the direction of flow, in the annular space 14 between the heating gas tubes and the steam guide tubes and finally reaching the steam space from where it is discharged through the nozzle 7. Cooling of the heating gas, and, consequently, superheating of the steam depends on sizing the upper part of the heating gas tubes and of the annular space. Adequate cooling is safely achieved because, according to this invention, the hot heating gas tubes 2 are contacted only by flowing steam of high velocity. There is no risk of thermal shock with consequent corrosive attack.

The tubes are shown on the drawing as straight lengths without particular design considerations concerning the heat transfer surfaces. in order to accommodate a larger heat transfer area in a steam generator of given dimensions, it is possible to deviate from the straight design and arrange the heating gas tubes 2 in helical or coiled form.

As it is imperative to prevent the steam guide tubes 13 from being subject to vibration that might be caused by the steam flow, their lower ends may be provided with retaining pins 15, as shown in FIG. 2. These pins fit into recesses or bulges 16 provided on the protective tubes 12.

What I claim is:

l. A steam generator comprising an upright closed housing provided with a gas inlet at the lower end and a gas outlet at the upper end thereof, a lower tubesheet in the lower portion of said housing, an upper tubesheet in the upper portion of said housing, a plurality of spaced heating gas tubes fixed at their ends in said tubesheets respectively enabling gas passage from said inlet to said outlet, an intermediate tubesheet spaced a relatively short distance below said upper tubesheet to form a steam space, said intermediate tubesheet being apertured to enable said gas tubes to pass freely therethrough, a steam outlet in said housing for venting said steam space, a water inlet in said housing adjacent to and above said lower tubesheet, steam guide tubes for said heating tubes secured at their upper ends in said intermediate tubesheet, spaced from said heating tubes and extending for a substantial portion of the length thereof, and protective cups open at the top freely to receive the lower end portions of said steam guide tubes, and fitting said gas tubes in liquid tight fashion, whereby, water in the lower end portion of said housing forms steam which passes into the protective cups and upwardly through said steam guide tubes, thence to the steam space, and finally discharges through said steam outlet.

2. A steam generator as claimed in claim 1, in which said intermediate tubesheet is spaced from the water level in said housing to provide a steam space of appreciable volume.

3. A steam generator as claimed in claim 1, comprising means for securing the lower ends of said steam guide tubes to said protective cups respectively to militate against relative vibratory movements.

4. A steam generator as claimed in claim 3, in which said securing means comprises retaining pins radiating from one of said steam guide tubes and protective cups and recesses to receive such pins in the other. 

1. A steam generator comprising an upright closed housing provided with a gas inlet at the lower end and a gas outlet at the upper end thereof, a lower tubesheet in the lower portion of said housing, an upper tubesheet in the upper portion of said housing, a plurality of spaced heating gas tubes fixed at their ends in said tubesheets respectively enabling gas passage from said inlet to said outlet, an intermediate tubesheet spaced a relatively short distance below said upper tubesheet to form a steam space, said intermediate tubesheet being apertured to enable said gas tubes to pass freely therethrough, a steam outlet in said housing for venting said steam space, a water inlet in said housing adjacent to and above said lower tubesheet, steam guide tubes for said heating tubes secured at their upper ends in said intermediate tubesheet, spaced from said heating tubes and extending for a substantial portion of the length thereof, and protective cups open at the top freely to receive the lower end portions of said steam guide tubes, and fitting said gas tubes in liquid tight fashion, whereby, water in the lower end portion of said housing forms steam which passes into the protective cups and upwardly through said steam guide tubes, thence to the steam space, and finally discharges through said steam outlet.
 2. A steam generator as claimed in claim 1, in which said intermediate tubesheet is spaced from the water level in said housing to provide a steam space of appreciable volume.
 3. A steam generator as claimed in claim 1, comprising means for securing the lower ends of said steam guide tubes to said protective cups respectively to militate against relative vibratory movements.
 4. A steam generator as claimed in claim 3, in which said securing means comprises retaining pins radiating from one of said steam guide tubes and protective cups and recesses to receive such pins in the other. 